This non-provisional application claims priority under 35 U.S.C. xc2xa7119(a) on Patent Application No. 84999/2000 and Patent Application No. 85000/2000, both of which were filed in Korea on Dec. 29, 2000 and are herein incorporated by reference.
1. Field of the Invention
The present invention relates to an optical pick-up apparatus, and more particularly to a laser diode unit for an optical pick-up apparatus capable of applying a laser beam emitted from a laser diode to an optical disc and a monitor photodiode (PD) using an integral optical system.
2. Description of the Related Art
Generally, optical pick-up devices have an arrangement illustrated in FIG. 1.
FIG. 1 is a schematic view illustrating the structure of an optical system used in a general optical pick-up device.
Referring to FIG. 1, the optical pick-up device includes a laser diode 101 for emitting a laser beam, a monitor PD 102 for adjusting recording power, and a focusing lens 103 for focusing the laser beam emitted from the laser diode 101 onto the monitor PD 102. The optical pick-up device also includes a collimator lens 104 for converting the laser beam emitted from the laser diode 101 into a collimated beam, a mirror 105 for changing an optical path of the collimated beam emerging from the collimator lens 104 to allow the collimated beam to be irradiated onto an optical disc 107, and an objective lens 106 for focusing the collimated beam, reflected by the mirror 105, onto the optical disc 107 in the form of a beam spot.
In this case, the collimator lens 104, mirror 105, and objective lens 106 form an L-shaped optical system.
Now, the operation of the optical pick-up device having the above mentioned arrangement will be described. A laser beam emitted from the laser diode 101 is converted into a collimated beam by the collimator lens 104. The optical path of the collimated beam is changed by the mirror 105 so that the collimated beam is fed to the objective lens 106. The collimated beam is then focused onto a desired point on the optical disc 107 by the objective lens 106. Meanwhile, a part of the laser beam emitted from the laser diode 101 is converged by the focusing lens 103, and then made incident to the monitor PD 102 so as to provide information required for adjustment of optical recording power.
In the conventional optical pick-up device illustrated in FIG. 1, however, it is difficult to provide a slim structure because the optical system used in the pick-up device has an L-shaped structure.
In other words, the optical system used in this pick-up device should have a collimator lens in order to convert the laser beam emitted from the laser diode, that is, a divergent beam, into a collimated beam. The optical system should also have a mirror for changing the optical path of the collimated beam to allow the collimated beam to be fed to the objective lens adapted to focus the collimated beam onto the optical disc. For this reason, the optical system must have an L-shaped structure. In addition to the provision of the collimator lens and mirror, the pick-up device should also have a separate arrangement including a monitor PD and a focusing lens for the monitor PD. As a result, it is difficult for the optical pick-up device to have a slim structure.
Therefore, the present invention has been made in view of the above mentioned problems, and an object of the invention is to provide a package type laser diode unit capable of emitting a laser beam in the form of a collimated beam.
Another object of the invention is to provide a laser diode unit capable of converging a laser beam to allow the laser beam to be focused onto an optical disc, thereby realizing an optical pick-up having a super-slim structure.
Another object of the invention is to provide a laser diode unit having an integral optical system, thereby being capable of providing an optical pick-up having a slim, simple, and miniature structure.
In accordance with one aspect, the present invention provides a laser diode unit for an optical pick-up apparatus comprising: a laser diode for emitting a laser beam; a monitor photodiode for controlling recording optical power; an optical disc on which data is written by the laser beam or from which data is read by the laser beam; and a lens module for reflecting a part of the light beam emitted, in the form of a divergent light beam, from the laser diode, thereby focusing the light beam onto the optical disc, the lens module also serving to transmit the remaining part of the light beam therethrough, thereby allowing the transmitted light beam to be converged by the monitor photodiode.
The lens module may comprise a diffraction grating face for diffracting the divergent light beam emitted from the laser diode, a holographic optical element face for reflecting a part of the divergent light beam while transmitting the remaining part of the divergent light beam to the monitor photodiode, and a lens face arranged to face the optical disc and adapted to output the light beam reflected by the holographic optical element face.
The diffraction grating face may be arranged to face the laser diode while being integral with the laser diode. Alternatively, the diffraction grating face may face the laser diode while being spaced apart from the laser diode by a desired distance.
The lens face may have a structure for outputting the light beam reflected by the holographic optical element face in the form of a collimated light beam. Alternatively, the lens face may have a structure for converging the light beam reflected by the holographic optical element face.
In accordance with another aspect, the present invention provides a laser diode unit for an optical pick-up apparatus comprising: a laser diode for emitting a laser beam; a monitor photodiode for controlling recording optical power; an optical disc on which data is written by the laser beam or from which data is read by the laser beam; a first optical power lens face arranged to face the laser diode and adapted to reflect the light beam emitted, in the form of a divergent light beam, from the laser diode; a holographic optical element face for reflecting a part of the divergent light beam while transmitting the remaining part of the divergent light beam to the monitor photodiode; and a second optical power lens face arranged to face the optical disc and adapted to converge the light beam reflected by the holographic optical element.
The second optical power lens face may be a pseudo objective lens.
In accordance with another aspect, the present invention provides an integral optical package comprising: a diffraction grating face formed with a plurality of horizontally-extending diffraction grating portions, the diffraction grating face facing a laser diode while being attached to the laser diode; a holographic optical element defined with a thin diffraction region and a dense diffraction region arranged in a vertical direction, the holographic optical element being attached to a monitor photodiode; and a focusing lens face for converging a light beam reflected by the holographic optical element.
In accordance with another aspect, the present invention provides an integral optical package comprising: a diffraction grating face formed with a plurality of horizontally-extending diffraction grating portions; a holographic optical element defined with a thin diffraction region and a dense diffraction region arranged in a vertical direction, the holographic optical element being attached to a monitor photodiode; and a collimating lens face having a lens curvature for transmitting a light beam, reflected by the holographic optical element, in a collimated state.